Data reader with spin filter

ABSTRACT

A data reader may be configured with at least a detector stack positioned on an air bearing surface and consisting of a spin accumulation channel continuously extending from the air bearing surface to an injector stack. The injector stack can have at least one cladding layer contacting the spin accumulation channel. The at least one cladding layer may have a length as measured perpendicular to the ABS that filters minority spins from the detector stack.

SUMMARY

Assorted embodiments configure a data reader to have at least a detectorstack positioned on an air bearing surface and consisting of a spinaccumulation channel continuously extending from the air bearing surfaceto an injector stack. The injector stack has at least one cladding layercontacting the spin accumulation channel. The at least one claddinglayer has a length as measured perpendicular to the ABS that filtersminority spins from the detector stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a line representation of a portion of an example datareader arranged in accordance with assorted embodiments.

FIGS. 2A and 2B respectively display cross-sectional linerepresentations of portions of an example data reader configured inaccordance with some embodiments.

FIG. 3 is a cross-sectional line representation of a portion of anexample data reader arranged in accordance with various embodiments.

FIG. 4 illustrates a line representation of a portion of an example datareader configured in accordance with assorted embodiments.

FIGS. 5A-5C respectively show line representations of portions of anexample data reader constructed and operated in accordance with someembodiments.

FIGS. 6A-6C respectively display block representations of portions of anexample data reader configured in accordance with some embodiments.

FIGS. 7A and 7B respectively, depict line representations of an exampledata storage system that may employ a data reader in variousembodiments.

FIG. 8 depicts a block representation of an example data storage systemin which a data reader can be utilized in accordance with someembodiments.

FIG. 9 provides a flowchart of a data reader fabrication routine carriedout in accordance with various embodiments.

DETAILED DESCRIPTION

Meeting consumer and industry demand for larger data capacity and fasterdata access in reduced form factor data storage devices has correspondedwith minimizing the physical size of data storage components while moredensely positioning data bits on a data medium. Such reduced componentsize can stress the fabrication and accuracy of the component. Hence,there is a continued goal of providing smaller data storage componentsthat are stable and provide optimized performance.

The advancement of magnetic reader technology to meet these goalsdemands reduced scaling of readers that will render conventional datareading, such as perpendicular magnetoresistance-based data readers,inapplicable. The emerging field of spintronics embodies the marriage ofmagnetic and electronic physics in a solid-state device whereby electronspins may be influenced by both magnetic and electric fields. Theconception of spintronic devices for magnetic read heads is thereforeesteemed to provide a viable path for next-generation data readers.

Although a lateral spin valve data reader is interesting for advancedmagnetic reader embodiments, the detection signals have been less thanpreferred. Therefore, assorted embodiments leverage the spin-nature ofconduction electrons in a lateral spin valve data reader to increasedetection signals and optimize performance. A lateral spin valve datareader can provide drastic shield-to-shield spacing (SSS) reduction thatallows the reader to be utilized in greater data track densityenvironments. The reduced SSS is further suitable for combination withother data readers in a transducing head.

With a lateral spin valve, a data reader inherently relies on thetraversal of a spin-coherent (polarized) current from a magneticinjector lead into and across a non-magnetic channel layer to a detectorlead. During the spin-injection process, only a fraction of totalinjected electron spins maintain their spin coherence. The efficiency bywhich spin-polarized electrons maintain their initial polarized stateafter injection into the non-magnetic channel has been termed spininjection efficiency and denoted by the parameter, α. Spin injectionefficiency is 30% for transparent channels with no tunnel barrier and30-40% for Ni- and Co-based alloys, which indicates that a majority ofspins suffer randomization processes during injection.

During and following the injection of spin-polarized electrons into thenon-magnetic channel, the traversal of spin current across the channelmedium unavoidably encounters various scattering centers that scatterelectron momentum. Some of these momentum scattering processes lead torandomization of the electron spin ensemble, which can be termedde-coherence or spin-flipping. The effect of the randomization ofelectron spin in the lateral spin valve channel is fewer spin-coherentelectrons that make it to the detector contact, which ultimately resultsin a diminished signal level at the detector lead. Therefore, tomaximize the detector signal, a lateral spin valve must minimize thespin scattering centers encountered during their travel to the detectorlead as well as maximize the spin-coherent distribution of electrons inthe channel by increasing spin injection efficiency.

FIG. 1 displays a line representation of an example data reader 100configured to filter out the ‘reverse-oriented’ minority spin populationinjected into the channel and maximize the ‘forward-oriented’ majorityspin population in order to maximize the detected signal of the datareader 100. The data reader 100 is a lateral spin valve with anon-magnetic channel 102 continuously extending from an air bearingsurface (ABS), where a magnetic detector 104 is positioned, to amagnetic injector 106 that is separated from the ABS. A magnetic spinfilter 108 contacts the channel 102, opposite the injector 106. Whilenot limiting, the injector 106, detector 104, and filter 108 can beconstructed of similar or dissimilar materials, such as Heusler alloys,dilute magnetic semiconductors, Co, Fe, Ni, and alloys thereof.

Whereas the filter 108 may be constructed of any number of magnetic andnon-magnetic layers, various embodiments set fixed magnetizations 110 infirst 112 and second 114 ferromagnetic layers with a magnetic pinninglayer 116. It is contemplated that the pinning layer is a permanentmagnet or antiferromagnetic (AFM) material that maintains theferromagnetic layers 112 and 114 in predetermined orientations. In thenon-limiting example of FIG. 1, the filter 108 is a syntheticantiferromagnet (SAF) where the ferromagnetic layers 112 and 114 areseparated by a non-magnetic spacer layer 118 to provideantiferromagnetic coupling that sets the fixed magnetizations 110 atopposite orientations.

By tuning the configuration of the filter 118, the fixed magnetization110 proximal the channel 102 has an opposite polarity from the injectormagnetization 120. When a partially spin-polarized current is injectedinto the channel 102, the spins that align with the magnetic filter 108will experience a low energy barrier into the filter lead and arereadily absorbed by the filter 108, which leaves behind a higherpercentage of electrons with spins aligned in the majority direction ofthe injector 106.

It is noted that a pair of side shields 122 are positioned on the ABSand separated from the detector 104. The side shields 122 may bemagnetic or non-magnetic and increase the data bit resolution of thedata reader 100. As shown, the filter 108 is separated from the ABS andthe channel 102 has a thickness 124 that is configured to allowefficient transmission of current from the injector 106 to the detector104. With the filter 108 configured as a SAF, one or more annealingoperations can set at least the magnetic orientations 110. That is, asingle anneal could serve to set both the injector 106 and ferromagneticlayers 112/114.

FIGS. 2A and 2B respectively display line representations of portions ofan example data reader 130 constructed and operated in accordance withvarious embodiments. In FIG. 2A, the detector 104 comprises a singlemagnetically free layer 132 that contacts the channel 102. When a readcurrent is introduced through the injector 106 or directly into thechannel 102, minority spins are absorbed by the filter 108, asillustrated by line 134 of FIG. 2B, and majority spins are allowed topropagate down the channel 102 towards the detector 104, as illustratedby line 136.

Increasing the fractional number of majority spins in the channel 102effectively increases the spin injection efficiency and the detectorsignal level. The detector signal level is proportional to themagnetoresistance of the detector junction and therefore, approximatelythe square of the injection efficiency, as given by equation 1:

$\begin{matrix}{\mspace{11mu} {{\Delta \; R_{NL}} = {\frac{4\; \alpha^{2}R_{FM}^{2}}{\left( {1 - \alpha^{2}} \right)^{2}R_{N}} \cdot \frac{^{\frac{- d}{\lambda_{N}}}}{\left\lbrack {1 + \frac{{zR}_{FM}}{\left( {1 - \alpha^{2}} \right)^{2}R_{N}}} \right\rbrack^{2} - ^{\frac{{- 2}d}{\lambda_{N}}}}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where is

$\frac{\left( {I_{\uparrow} - I_{\downarrow}} \right)}{\left( {I_{\uparrow} + I_{\downarrow}} \right)}$

is a phenomenological parameter describing spin injection efficiency viacurrent polarization, R_(FM) is the spin resistance associated with theferromagnetic metal, R_(N) is the spin resistance associated with thenon-magnetic channel, d is the physical separation between the injectorand detector leads and is the spin diffusion length in the non-magneticchannel. It is noted that equation 1 pertains to a spin valve operatingin a non-local configuration where spin accumulation at the detector 104is solely responsible for the detector signal. When spin current alsoincludes a drift component (local configuration) the analyticalmagnetoresistance picture is less clear.

It is noted that the filter 108 is in direct contact with the channel102. The absence of a tunnel barrier between the channel 102 and filter108 can promote absorption of minority spins 134. For clarity, the term“majority spin” herein means spin that matches the polarity of theinjector magnetization 120 while the term “minority spin” herein meansspins that match the filter magnetization 110.

FIG. 3 is a cross-sectional line representation of a portion of anexample data reader 150 arranged in accordance with some embodiments toincrease the filtering of minority spins. The channel 102 of the datareader 150 contacts a first filter 152 configured as a SAF and a secondfilter 154 configured as an exchange coupled lamination. The SAF firstfilter 152 contacts the ABS and has a length 156 that continuouslyextends from the detector 104 to the injector 106. Although the filterlength 156 can be adjusted, increased filter contact with the channel102 heightens minority spin absorption.

The second filter 154 is positioned between, and electrically separatedfrom, the detector 104 and injector 106. The second filter 154 has alength 158 that is less than the length 160 of the channel 102. Thesecond filter 154 is constructed of a ferromagnetic layer 162 contactinga pinning layer 164, which may be an AFM or permanent magnet. As shown,the first 152 and second 154 filters have magnetic polarities 166oriented opposite to the injector magnetization 120 to promote minorityspin absorption and the propagation of majority spins to the detector104. It is contemplated that respective filters 152/154 can havematching configurations, such as materials, position, number of layers,and size, or have dissimilar configurations. Regardless of theconfiguration of the filters 152/154, the tuned magnetic polarities 166proximal the channel 102 provide increased injection efficiency anddetector signal level.

FIG. 4 is a cross-sectional line representation of an example datareader 170 configured in accordance with some embodiments to provideoptimized data sensing performance with a reduced physical size. Thedata reader 170 has a detector 104 disposed between top 172 and bottom174 shields. The detector 104 contacts a barrier layer 176 between thechannel 102 and the magnetically free layer 132. Such barrier layer 176can be tuned for material and size to provide a measurablemagnetoresistance when a sensing current 178 passes through the detector104. The size of the barrier layer 176 may be reduced or eliminated tominimize a shield-to-shield spacing 180 between the shields 172 and 174.

While the SSS 180 can be reduced by moving the injector 106 away fromthe ABS, the size of the injector 106 may correspond with notches inone, or both shields 172 and 174. It is noted that the respectivenotches can be filled with insulating material to electrically separatethe injector 106 from the detector 104 and shields 172/174. That is, theinjector 106 and detector 104 are electrically isolated from one anotherexcept through the channel 102.

The injector 106 may have one or more electrodes 182 that act as aterminal to bring a read signal into the channel 102. In accordance withvarious embodiments, the injector 106 has a length 184 that is less thanthe length 186 of the filter 108. The filter length 186 can be tuned toprovide an optimized balance of minority spin absorption withoutinhibiting the efficiency of majority spin transmission from theinjector 106 to the detector 104.

FIGS. 5A, 5B, and 5C respectively convey different line representationviews of portions of an example data reader 200 arranged in accordancewith assorted embodiments. FIG. 5A is a cross-sectional view of a2-terminal lateral spin valve with first 202 and second 204 shieldsserving dual purposes of absorbing stray magnetic fields and passingread current from the injector 106 to the detector 104. As such, thereader 200 has an injector terminal 206 and a detector terminal 208 thatmaintain the electrical isolation of the injector 106 and detector 104except through the channel 102.

The channel 102 contacts first 210 and second 212 filter laminationsthat can each be configured with fixed magnetizations of a predeterminedorientation that absorbs minority spins relative to the injector 106magnetization orientation. The filter laminations 210/212 can beconstructed as SAF or exchange coupled structures that are electricallyisolated from the injector 106 and detector 104. The respective filterlaminations 210/212 can have the same, or different lengths as measuredperpendicular to the ABS as well as the same, or different, distancesfrom the respective injector 106 and detector 104.

FIG. 5B displays a top view of the reader 200 from the second shield 204downward towards the first filter lamination 210 and magnetically freelayer 132 of the detector 104. An ABS view of the reader 200 in FIG. 5Cillustrates how the second filter 212 extends from the ABS towards theinjector 106 while remaining electrically isolated from the first shield202. The ability to contact the channel 102 with multiple filterlaminations 210/212 can optimize data reader 200 performance byincreasing the injection efficiency compared to a channel having nofilter and scattering centers that degrade injection efficiency anddetector signal level.

FIGS. 6A-6C respectively display block representations of portions ofexample lateral spin valve data readers 220 arranged in accordance withvarious embodiments. In FIG. 6A, the non-magnetic spin channel 102continuously extends from the ABS to contact the detector 104 andinjector 106. The injector 106 is separated from the ABS and allows thesize of the reader 220 to be smaller than if the injector 106 waspositioned on the ABS. To sense external data bits with the data reader100, a read signal, such as a current is passed from the injectorterminal 222 to a detector terminal 224 through the spin channel 102.

Although the 2-terminal data reader of FIG. 6A can provide accurate datasensing, assorted embodiments add a channel terminal 226, as shown inFIG. 6B. The addition of the channel terminal 226 can allow fordifferent biasing and read signal schemes to tune how the data reader220 responds to encountered data bits. The capabilities of the datareader 220 may further be complemented by adding a secondary channelterminal 228 proximal the ABS, as shown in FIG. 6C. The 4-terminalconfiguration of FIG. 6C adds complexity, but allows for terminals 222and 226 to be utilized as pathway through the channel 102 and injector106 and for terminals 224 and 228 to be utilized as a pathway throughthe detector 104 and channel 102.

The ability to configure a data reader 220 with multiple terminals canprovide a diverse variety of operating capabilities. However, a datareader is not limited to a single detector 104, injector 108, ornon-magnetic spin channel 102. FIGS. 7A and 7B respectively displaycross-sectional line representations of portions of an exampletransducing head 240 configured with multiple data readers 242 and 244in accordance with some embodiments. By positioning the two data readers242 and 244 together on the ABS, the transducing head 240 can employsuccessive, redundant, or simultaneous sensing of data bits, such aswith two-dimensional data recording (TDMR) environments.

It is noted that while two data readers 242 and 244 are shown, sucharrangement is not limiting and any number of readers can be physicallyconnected on the ABS. As shown, the first 242 and second 244 datareaders are separated by a non-magnetic insulating layer 246 that can betuned for thickness 248 to electrically and magnetically isolate thefirst data reader 242 from the second data reader 244. The insulatinglayer 246 can be disposed between first 250 and second 252 mid-shieldsthat further isolate the respective data readers 242 and 244.

In some embodiments, each reader 242 and 244 is configured with a spinfilter 254 that may be configured with matching, or be dissimilar,materials, numbers of layers, position, and length to increase the spininjection efficiency of the transducing head 240. As a non-limitingexample, the spin filter 254 of the first data reader 242 can have alarger length, as measured perpendicular to the ABS, than the spinfilter 254 of the second data reader 244. By tuning the configuration ofthe respective spin filters 242 and 244 to be different, the performanceof the data readers 242 and 244 will be different, which may be desiredin some data storage environments. While the arrangement of theconstituent aspects of the respective data readers 242 and 244 can betuned match or be different, the orientation of the data readers 242 and244 may also be tuned.

FIG. 7A illustrates how the data readers 242 and 244 can be configuredto provide a spacing distance 256, as measured from the top of the firstfree layer (FL1) of the first data reader 242 to the bottom of thesecond free layer (FL2) of the second data reader 244. The spacingdistance 256 corresponds with the data bit resolution of the transducinghead 240. FIG. 7B illustrates how the same spacing distance 256 can beachieved by flipping the orientation of the second data reader 244relative to the first data reader 242. The ability to alter theorientation of the respective data readers 242 and 244 can complementthe tuned configuration of the spin filters 254 to optimize data sensingperformance for the transducing head 240.

FIG. 8 depicts a block representation of an example data storage system260 in which a data reader can be utilized in accordance with someembodiments. The system 260 can employ any number of data storagedevices 262 individually and collectively. While not limiting orrequired, the data storage device 262 of FIG. 8 has a local controller264 that directs operations between at least one transducing head 266and one or more data media 268 to store and retrieve data. It is notedthat the data storage device 262 can be configured with volatile and/ornon-volatile memory structures that rotate or are solid-state, such asin a hybrid hard disk drive with both rotating and solid-statenon-volatile memory.

Each transducing head 266 of the data storage device 262 has at leastone data writer 270 and data reader 272 that can operate independentlyand concurrently to program one or more data bits 274 resident in a datamedium 268. The local controller 264 facilitates operation of thetransducing head 266 by rotating the data medium 268 via a spindle motor276 to create an air bearing between the data bits 274 anddata-accessing writer 270 and reader 272. The local controller 264 canoperate alone and in combination with one or more remote hosts 278, suchas a processor, server, or node, that is connected to the data storagedevice 262 via a wired or wireless network 280.

FIG. 9 provides a flowchart of an example data reader fabricationroutine 290 that is carried out in accordance with various embodimentsto construct a lateral spin valve data reader that is subsequentlyutilized to sense data bits in a data storage device of a data storagesystem. Routine 290 begins by depositing a magnetic injector adjacent toand separated from a first filter lamination in step 292. The firstfilter lamination may be a SAF or exchange coupled structure thatprovides a fixed magnetization along. Step 292 may further configure thefirst filter lamination with a length that may continuously extend tothe ABS and/or be greater than the length of the injector.

Next, step 294 creates a non-magnetic spin channel in contact with boththe injector and first filter lamination. The spin channel is then usedas a substrate for the detector and second filter lamination to bedeposited on in step 296. The second filter lamination may beconstructed to match, or be dissimilar to, the first filter laminationwith regard to the number of layers, materials, and thicknesses toprovide an additional fixed magnetization in contact with the spinchannel. The material of the various magnetic aspects of the data readercan be selected from alloys of Co, Ni, and Fe as well as from Heusleralloys and dilute magnetic semiconductor materials.

Although not required, the various aspects of the data reader canundergo one or more annealing operations in step 298 that expose thematerials to elevated temperatures and a set magnetization orientation.It is contemplated that annealing operations can be conducted onindividual components of the data reader, such as the first filterlamination, without exposing all magnetic aspects of the reader to thesame annealing conditions.

It is noted that the various steps of routine 290 are not limiting andany portion can be modified or removed just as additional steps anddecisions can be incorporated. For example, additional steps can depositshields in contact with the respective injector and detector or depositinsulating material about the first and second filter laminations toelectrically isolate them from the injector and detector. As anotherexample, the first, or second, filter lamination may be omitted from thedata reader. The routine 290 may further be configured as a 2, 3, or 4terminal sensor, as generally illustrated in FIGS. 6A-6C, via one ormore fabrication steps.

Through the formation of at least one spin depolarizing structurecontacting a magnetic stack portion of a data reader, currentcontamination of the magnetic stack with spin polarization from adjacentmagnetic shields is reduced or eliminated. The ability to tune thematerial and thickness of the depolarizing layer allows for a range ofdifferent depolarizing structures, such as SAF laminations, andmaterials that are minority spin current carriers tuned for thickness toproduce a net zero spin polarization for the magnetic stack.Additionally, the magnetic nature of the depolarizing layer allows thedepolarizing structure to be present in a data reader, but notcontribute to the shield-to-shield spacing that plays a role in the databit resolution of a data reader, especially in reduced form factor datastorage devices.

While various embodiments have been directed to magnetic sensing, theclaimed technology can readily be utilized in any number of otherapplications, including solid state data storage applications.

1. An apparatus comprising a detector stack positioned on an air bearingsurface (ABS) and contacting a spin accumulation channel continuouslyextending from the ABS to an injector, the injector separated from thedetector, separated from the ABS, and contacting the spin accumulationchannel opposite a filter, the filter continuously extending from theABS with a length as measured perpendicular to the ABS that filtersminority spins from the detector.
 2. The apparatus of claim 1, whereinfilter contacts the spin accumulation channel opposite the detector. 3.The apparatus of claim 1, wherein the detector comprises a free magneticlayer positioned on the ABS, the detector not having a fixedmagnetization.
 4. The apparatus of claim 1, wherein the filter ismagnetized to a first direction and the injector is magnetized to asecond direction, the first and second directions being opposite.
 5. Theapparatus of claim 1, wherein the injector comprises a first materialand the filter comprises a second material, the first and secondmaterials being different.
 6. The apparatus of claim 5, wherein the spinaccumulation channel comprises a third material, the second and thirdmaterials being different.
 7. The apparatus of claim 1, wherein theinjector and detector each have a smaller length than the spinaccumulation channel and filter.
 8. The apparatus of claim 1, whereinthe filter continuously extends from the ABS on a side of the spinaccumulation channel opposite the injector and detector.
 9. Theapparatus of claim 1, wherein the filter is a synthetic antiferromagnet(SAF).
 10. The apparatus of claim 21, wherein the second filter contactsthe spin accumulation channel between the injector and detector.
 11. Theapparatus of claim 10, wherein the second filter is physically separatedfrom the detector and injector.
 12. The apparatus of claim 10, whereinsecond filter is separated from the ABS.
 13. The apparatus of claim 21,wherein the first and second filter each are configured to allowmajority spins to propagate towards the ABS via the spin accumulationchannel. 14-18. (canceled)
 19. A method comprising: positioning adetector on an air bearing surface (ABS), the detector contacting a spinaccumulation channel continuously extending from the ABS to an injector,the injector separated from the detector, separated from the ABS, andcontacting the spin accumulation channel, the filter having a length asmeasured perpendicular to the ABS; filtering minority spins from thedetector with the filter; and reading a data bit with the detector withmajority spins traveling through the spin accumulation channel, the databit stored on a data storage medium separated from the detector by anair bearing.
 20. The method of claim 19, wherein the minority andmajority spins are present in a read signal passing through the injectorto the spin accumulation channel.
 21. An apparatus comprising: a spinaccumulation channel continuously extending from an air bearing surface(ABS); a detector positioned on the ABS and contacting the spinaccumulation channel; an injector separated from the ABS and thedetector and contacting the spin accumulation channel; a first filtercontacting the spin accumulation channel and ABS and continuouslyextending from the ABS to a region of the spin accumulation channelproximal the injector; and a second filter electrically isolated fromthe detector and injector, the first and second filters each configuredto absorb minority spins from the spin accumulation channel.
 22. Theapparatus of claim 21, wherein the first filter contacts a first side ofthe spin accumulation channel and the second filter contacts a secondside of the spin accumulation channel, the first and second sides beingopposite.
 23. The apparatus of claim 21, wherein a reference layer ofthe first filter and a magnetic layer of the second filter respectivelycontact the spin accumulation channel, the reference and magnetic layersset to a common magnetization polarity.
 24. The apparatus of claim 23,wherein the reference layer is part of a synthetic antiferromagnet andthe magnetic layer contacts a fixed magnetization layer.
 25. Theapparatus of claim 21, wherein the first filter has a first length, thesecond filter has a second length, the injector has a third length, thedetector has a fourth length, each length measured perpendicular to theABS, the first length being greater than the second, third, and fourthlengths, respectively.